Understanding Load Balancing
Load Balancing is the practice of distributing network traffic or computational workloads between two or more computers. In modern applications, processing millions of requests simultaneously is common. A load balancer acts as a traffic controller, ensuring that all servers are utilized equally. It can be a physical device, a software process, or a virtualized instance running on specialized hardware.
How Load Balancers Work
When a user sends a request, the load balancer forwards it to a specific server. This process repeats for all incoming requests. Load balancers detect the health of backend resources and do not send traffic to servers that cannot fulfil requests. They improve performance and reliability by efficiently utilizing resources and preventing any single point of failure.
For example, imagine a restaurant where customers can choose their waiters. Some waiters might be overloaded while others remain idle. If a manager (load balancer) assigns customers to waiters, all waiters work efficiently, ensuring balanced workloads.
In response to increased network traffic, a load balancer can activate additional servers to meet demand. Conversely, if traffic decreases, the load balancer can reduce the number of active servers.
Load Balancing Algorithms
Load balancers use various algorithms to determine which server handles each request. These algorithms offer different capabilities and benefits for various use cases.
- Round Robin: This simple method rotates through servers, forwarding each new request to the next server in line.
- Weighted Round Robin: Servers are assigned weights based on their capacity. More powerful servers receive more requests.
- IP Hash: The client’s IP address is hashed to create a key, determining the server for the request.
- Least Connections: Requests go to the server with the fewest active connections, balancing the load.
- Weighted Least Connections: This method considers both server weights and active connections, directing requests to the server with the lowest connection-weight ratio.
- Least Response Time: Requests are sent to the server with the fastest response time and the fewest active connections.
Benefits of Load Balancing
- Improved Performance: Distributing workloads across multiple resources reduces network latency and enhances system performance.
- High Availability: By eliminating single points of failure, load balancers ensure higher availability and fault tolerance.
- Application Security: Load balancers can add security layers with features like SSL encryption, web application firewalls (WAF), and multi-factor authentication (MFA), protecting against threats like DDoS attacks.
- Scalability: Load balancers handle multiple requests concurrently, preventing server overload and allowing for seamless scaling by adding or removing servers as needed.
Types of Load Balancers
- Global Server Load Balancers: Route traffic across multiple geographical locations, assigning user requests to the closest server and redirecting traffic in case of server failure.
- Application Load Balancers: Route API requests based on application content such as URLs, SSL sessions, and HTTP headers.
- Network Load Balancers: Examine IP addresses and other network information to optimally redirect traffic, reducing latency across local and wide area networks.
